Referring to FIG. 1, a conventional power supplying device 1 is shown to include a rectifying and boosting conversion circuit 11, a series connection of a diode (D1) and an output capacitor (C1), and a DC-to-DC converter 12. The rectifying and boosting conversion circuit 11 receives an alternating current (AC) input voltage (v) from an input power source 10, and rectifies and boosts the AC input voltage (v) so as to output an output voltage (Vr1) at an output side thereof. The series connection of a diode (D1) and an output capacitor (C1) is coupled to the output side of the rectifying and boosting conversion circuit 11 for receiving the output voltage (Vr1) therefrom, and rectifies and filters the output voltage (Vr1). The DC-to-DC converter 12 is coupled in parallel to the output capacitor (C1) for receiving a voltage (Vr2) (C1), and converts the voltage (Vr2) into one or more DC voltages (V11-V1n) which are to be supplied to one or more backend loads (not shown).
In such a configuration, when a brownout condition suddenly or temporarily occurs in the AC input voltage (v) from the input power source 10, typically, by increasing the capacitance of the output capacitor (C1) the working voltage range of the DC-to-DC converter 12, the conventional power supplying device 1 may maintain normal supply of the DC voltages (V11-V1n) within a regulation period, thereby ensuring normal operations of the backend loads, for example, storing information. However, increasing the capacitance of the output capacitor (C1) may increase the volume of the output capacitor (C1) and power consumption of the conventional power supplying device 1. In addition, increasing the working voltage range of the DC-to-DC converter 12 may reduce efficiency of conversion from the voltage (Vr2) to DC voltage(s) (V11-V1n) by the DC-to-DC converter 12 in normal operation thereof.